The present invention relates to a resistance value adjusting method for adjusting the electric resistance value of a resistor which has a resistive film formed on a plurality of linear conductive films, and an electric contact which is slid in a width direction of the linear conductive films to change the resistance value.
Conventionally, a resistor for a fuel gauge is known for presenting a driver the amount of fuel remaining in a fuel tank equipped, for example, in a vehicle. As illustrated in FIG. 3, this resistor for a fuel gauge has a plurality of linear conductive films 101 formed on a substrate in a film shape such that they are arranged in parallel, and a resistive film 102 formed on the linear conductive films 101 in a film shape. Generally, the fuel gauge is required to have a resolution of approximately 40-60, and therefore the resistive film 102 must be formed to support the resolution.
In such a resistor for a fuel gauge, an electrode is formed, for example, at an end 101a of the right-most linear conductive film of the plurality of linear conductive films 101, and an electric contact is slid in a width direction on portions of the linear conductive films 101 in which the resistive film 102 is not formed, thereby establishing an electric conduction between the electric contact and electrode.
In the resistor for a fuel gauge, in order to provide a different resistance value when the electric contact comes into contact with a different linear conductive film 101, portions of the resistive film 102 existing between the respective linear conductive films 101 are trimmed to form trimmed portions 103.
In this manner, as the electric contact comes closer to the end 101a of the linear conductive film, for example, due to a gradually reduced amount of fuel in the fuel tank, the resistive file between the electric contact and the end 101a of the linear conductive film is reduced to cause a lower resistance value, so that a larger current flows, and a display on the fuel gate is changed in accordance with the current value.
The aforementioned resistor for a fuel gauge has several points such as E (EMPTY) point, xc2xc point, xc2xd point, xc2xe point, F (FULL) point and the like as management points which function as marks for presenting the amount of remaining fuel to the driver.
As a fuel gauge, a needle for indicating the amount of remaining fuel preferably exhibits a linear characteristic, for which all portions of the resistive film between the respective linear conductive films 101 are trimmed to form the trimmed portions 103. Therefore, with the conventional resistor for a fuel gauge, a trimming step for adjusting the resistance value must be performed in all the portions of the resistive film between the respective linear conductive films 101, resulting in a low working efficiency.
Thus, the present invention has been made in view of the foregoing circumstance, and it is an object to provide a resistance value adjusting method which is capable of efficiently adjusting the resistance value of a resistive film in a resistor.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
(1) A method of adjusting a resistance value of a film resistor which includes a plurality of linear conductive films formed in parallel on a substrate, and a resistive film formed over portions of the plurality of linear conductive films in a width direction of the linear conductive films, wherein an electric contact is slid over the plurality of linear conductive films to change a detected resistance value, the method comprising the steps of:
defining, as a single resistive element, a portion of the resistive film formed over a first linear conductive film formed at a position at which a first resistance value is detected when the electric contact is slid thereto, and a second linear conductive film formed at a position at which a second resistance value is detected when the electric contact is slid thereto, the first and second linear conductive films interposing a plurality of the linear conductive films;
trimming a portion of the resistive element at opposite sides of the first linear conductive film in a longitudinal direction substantially perpendicular to the width direction to form first and second trimmed portions; and
trimming a portion of the resistive element from an end of the second trimmed portion in the width direction toward the second linear conductive film to form a third trimmed portion.
(2) The method according to (1), wherein the first trimmed portion is trimmed so as to adjust a resistance value, detected when the electric contact is slid to the first linear conductive film, to the first resistance value.
(3) The method according to (1) or (2), wherein the second trimmed portion has a length which is determined based on the number of the linear conductive films formed between the first and second linear conductive films.
(4) The method according to (1) through (3), wherein the third trimmed portion is trimmed so as to adjust a resistance value detected when the electric contact is slid on the linear conductive films formed between the first and second linear conductive films.
(5) The method according to (1) further comprising the step of:
trimming a portion of the resistive element in the vicinity of the second linear conductive film in the longitudinal direction to form a fourth trimmed portion.
(6) The method according to (5), wherein the fourth trimmed portion is trimmed so as to adjust a resistance value, detected when the electric contact is slid to the second linear conductive film, to the second resistance value.